The present invention is directed to directional control fluid valves such as those used in controlling hydraulic and other fluid systems. Specifically, the present invention relates to an improvement in such a directional control fluid valve which enables the actuation of valve spool movement within the valve in a manner to reduce pressure surges and shocks in the hydraulic systems associated with the valve while effecting actuation with fast acting actuators, such as alternating current (AC) solenoids.
The invention relates to a flexible drive member interposed between the spool of the valve to be moved and the actuating mechanism, which flexible drive member is capable of storing energy and thereby allows the spool to move at a different rate than the actuator applies motor force to the spool.
A problem experienced by hydraulic and other fluid systems is the creation of surges and shocks in a system during its operation because the control valve produces too fast an action. This problem has been recognized and addressed in the prior art. For example, in U.S. Pat. No. 3,324,890 to Witmore, et al., a dash pot is used which has a particular physical configuration to effect damping or retardation of motion of the valve element during specific portions of its travel. The Witmore device specifically is designed to not impede motion of the valve element in other portions of its travel.
Direct current (DC) solenoids have been used for actuation of directional control fluid valves in which slow spool movement is desirable because the armature of a DC solenoid can be shifted slowly, or even held in a position to keep the valve partially opened, without damage to the solenoid. However, if an AC solenoid is energized and the armature does not shift completely against the armature stop in a very short time (usually in less than 24 milliseconds), severe overheating and short circuiting of the solenoid coil will occur.
Since slow spool movement times of 50 milliseconds to 1000 milliseconds are common for antishock directional control fluid valves, AC solenoids have heretofore not been used to actuate such valves, even though the cost of AC solenoids is significantly less than the cost of comparably capable DC solenoids.
The flexible drive pin of the present invention allows an AC solenoid armature to complete its travel to the armature stop in its normal operating time without damage to the solenoid. The flexible drive pin stores energy during the travel of the solenoid armature and relatively slowly dissipates that stored energy to move the valve spool more slowly than the solenoid armature moved, thereby effecting an appropriate speed of movement of the valve spool to accomplish antishock actuation of the control valve while still enjoyinq the economic benefit of a significantly cheaper AC solenoid component.